Metal oxide hydrogen batteries, such as nickel oxide-hydrogen batteries, have seen wide use in aerospace applications because they are rechargeable, have an extremely long cycle life and provide a uniform output during the entire discharge cycle.
In the typical nickel oxide-hydrogen battery the positive electrodes are generally in the form of flat porous, sintered nickel plaques impregnated with nickel hydroxide, while the negative electrodes are formed of a fine nickel mesh screen having a catalyst, such as platinum black, bonded to one surface of the screen through a hydrophobic polymeric material. On discharge of the battery, hydrogen gas diffuses through the electrolyte surrounding the catalyst surfaces of the negative plates and becomes disassociated by the catalyst to the monoatomic form. The monoatomic hydrogen is ionized and combines with hydroxyl ions to form water with an electron being released in the process of forming each hydrogen ion. In addition, hydroxyl ions are formed at the positive electrode by the reaction of water with the available oxygen content of the nickel oxide. As a result of these reactions an electron current is produced in the exterior circuit.
On recharging the reaction is reversed, with the recharging being characterized by the regeneration of hydrogen gas at the negative electrode and the reoxidation of the nickel hydroxide at the positive electrode.
Due to the substantial gas pressures that are involved, the nickel oxide-hydrogen battery is contained within an outer pressure vessel. In the past the outer vessel has been composed of a nickel alloy, Inconel, due to the high strength and corrosion resistance of the Inconel alloy. However, Inconel is expensive and is difficult to fabricate into a closed cylindrical vessel. The practice has been to weld a thin Inconel sheath into a cylindrical shape and then weld dome shaped heads to the cylindrical shell.
The welding necessarily occurs after assembly of the battery cells and with the battery cells located within the vessel. The heat generated during the welding operation can adversely affect the performance of the battery and, therefore, steps have been taken in the past to isolate the welding heat from the cells through use of back up chills behind the weld joint and through use of laser beam welding which provides more concentrated or localized heating for the welding operation. Thus, the welding of the Inconel vessel requires a delicate and precisely controlled automated system which is extremely expensive and substantially increases the overall cost of the battery.
It has also been proposed to construct the pressure vessel for the battery of a welded, thin wall metal liner, which is in impervious to the passage of hydrogen gas, and a filament wound composite outer layer that is capable of withstanding the internal pressure. However, as the outer filament wound layer has different expansion characteristics than the thin metal liner, the internal pressure of the hydrogen gas may expand the metal liner beyond its yield, point and on release of the pressure, the metal liner may buckle.